Since long, ultrasound is used in the field of medical treatment. Recently, ultrasonic transducers, in particular high intensity focused ultrasound transducers, have been used for inducing lesions in tissue for therapeutic cancer treatment. Tissue lesion or tissue destruction is caused by cavitation effects of high intensity ultrasonic waves. This cavitation effect is linked to the formation of microscopic vapor bubbles in a region, where the pressure of liquid falls below its vapor pressure. When these bubbles collapse, energy is released leading to the destruction of neighboring tissue.
U.S. Pat. No. 5,601,526 describes a method and an apparatus for performing therapy using ultrasound for tissue disruption by means of cavitation and thermal effects. This document is concerned with providing a solution allowing a lesion in tissue to be treated, which is strictly limited to the focus point of the treatment device, and limiting or avoiding effects due to heat spreading around the focus point, with cavitation phenomena being limited exclusively to the focal point or to the focal region. For this, two types of ultrasonic waves are employed, one producing predominantly a thermal effect on the tissue, the other producing predominantly a cavitation effect on the tissue. Here, heating in the tissue occurs due to absorption of ultrasonic energy by frictional damping.
Also in analysis and diagnostics, ultrasound is more and more employed. For instance, the detection of infectious pathogens for prevention, early diagnosis and treatment of infectious diseases are based on the analysis of intracellular components, e.g. nucleic acids or specific molecules, of viruses or cells in a sample. Thus, one of the processing steps before analyzing the components is cell-lysis (cell breaking). Cell-lysis can be induced by means of high intensity focused ultrasound waves that generate cavitations in the sample. Upon implosion of these cavitations, enough energy is released to destroy the membranes of bacteria, viruses and cells and release their intracellular components.
Moreover, working with cells or small organisms involves a thorough control of environmental conditions, such as temperature. Temperature has wide influence, for instance, on the metabolism and the reproduction cycle of bacteria and cells. Hence, for most biological applications, temperature control is required. Yet, the space for adding more components to an experimental setup, such as heating means, is extremely limited, and in particular, since the trend is to minimize the sample volume for saving material costs and for accelerating the procedures. Therefore, a compact setup design is desirable.
However, when heating is performed due to ultrasonic energy absorption of a high intensity focused ultrasonic beam, the sample may be unintentionally influenced or sensitive components in a sample, such as membranes, may be damaged by local pressure and/or temperature peaks in the sample. In particular, it may be required to heat the sample before ultrasonic treatment without exposing the sample to acoustic pressure waves in order to get neat results. Thus, in diagnostics and analysis, it is often required to heat a sample without potentially manipulating or damaging it. Therefore, ways for gently heating a sample in a controlled way have to be found, being at the same time cost saving, space saving, easy to control and sufficiently fast.